Analgesic drugs for neuropathic and sympathetically maintained pain.

A variety of pharmacologic approaches to the management of pain due to nerve damage have been tried, with mixed results. Sympathetically maintained pain responds most commonly to sympathetic nerve blocks. Oral nifedipine may be a useful adjunct. Many-but not all-neuropathic pain patients experience relief from low-dose tricyclic antidepressants. When those drugs are not sufficient, the addition of an anticonvulsant, systemic local anesthetic, or both, to the antidepressant may be useful. Neuropathic pain with a major cutaneous component may respond well to topical therapy with the Substance P depletor capsaicin to reduce elevated prostaglandin levels. Topical therapy is most commonly used as an adjunct to systemic drugs. There is now good evidence that early treatment of acute herpes neuralgia with famciclovir may be effective in reducing postherpetic neuralgia. The role of opioids in chronic nerve pain is unclear. Most patients do not respond to these drugs, and should not receive them. Many patients with chronic neuropathic or sympathetically maintained pain need detoxification from opioids, sedative-hypnotics, and muscle relaxants. Some patients cannot carry out normal activities of daily living without opioids, however, and function well while taking low-dose, regularly scheduled opioids. The prognosis for successfully managing neuropathic and sympathetically maintained pain is greatly improved if appropriate therapy is initiated early in the course of the pain. When patients do not respond adequately to initial drug therapy, referral to an interdisciplinary pain management program for evaluation may be in order. Many neuropathic and SMP patients have complex pain syndromes which are most effectively managed through a coordinated, interdisciplinary approach. Careful attention to medical, pharmacologic, psychologic, and physical factors are the hallmarks of this type of treatment. The drugs now available provide marked relief to the majority of patients when therapy includes careful attention to the various dimensions of the pain syndrome. Although consistently effective drug therapy for all neuropathic and sympathetically maintained pain is not yet available, the probability of new NMDA antagonists being introduced in the next few years offers promise.